isFunction()

isFunction(value): value is Function

Checks if a value is a function.

note

Includes arrow functions, regular functions, async functions, and class constructors.

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Parameters

value: unknown

The value to check.

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Returns: value is Function

true if the value is a function, false otherwise.

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Since

1.0.0

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Example

isFunction(() => {});       // => true
isFunction(function() {});  // => true
isFunction(async () => {}); // => true
isFunction(class {});       // => true
isFunction({});             // => false

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How it works?

Type guard that checks if a value is a function.

Type Narrowing

Common Checks

Value	Result
() => {}	true
function() {}	true
async () => {}	true
class Foo {}	true
Array.isArray	true
{ call: () => {} }	false

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Use Cases

Execute callbacks safely 📌

Verify if a property is a callable function before invocation. Essential for event handlers and optional callback execution.

#execute#callbacks#safety#functions#invocation#optional

if (isFunction(props.onComplete)) {
  props.onComplete(result);
}

Resolve value-or-getter patterns

Handle props that can be either static values or functions returning values. Common pattern in React and configuration APIs.

#resolve#getter#patterns#dynamic#values#configuration

type MaybeGetter<T> = T | (() => T);

function resolve<T>(value: MaybeGetter<T>): T {
  return isFunction(value) ? value() : value;
}

const title = resolve(props.title); // Works with "Hello" or () => "Hello"